A pollutant control device for a National VI small-displacement non-EGR diesel engine

Abstract

The present invention discloses a pollutant control device for a China VI small-displacement non-EGR diesel engine, which is applied to diesel engines with a displacement below 2.3L and includes a supercharger turbine, an oxidation catalytic converter, a particulate trap, and a selective catalytic reduction converter that are sequentially connected to the exhaust end of the engine; the throat area of the supercharger turbine is greater than 230 mm<supgt;3< / supgt>, and the diameter of the turbine of the supercharger turbine is less than 44 mm. The beneficial effects of the present invention are as follows: By increasing the supercharger turbine with a large throat and a small turbine, the entropy increase in the turbine is increased, the outlet Mach number is increased, and the exhaust temperature of the engine is increased. Without installing an exhaust throttle valve, the exhaust temperature at low speed and low load can be increased, and the tailpipe NOx emission limit can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of diesel engines, and particularly to a pollutant control device for a non-EGR route. Background Art

[0002] When a diesel engine operates, the combustion in the combustion chamber will discharge a large amount of carbon monoxide (CO), incomplete combustion products, hydrocarbons (HC), unburned and incompletely burned fuel, lubricating oil and its cracking products and partial oxidation products, nitrogen oxides (NOx): a general term for various oxides of nitrogen (mainly NO and NO2) formed during the combustion process and after being discharged into the atmosphere, particulate emissions (PM): mainly soot, unburned fuel and liquid particles of lubricating oil, as well as other hydrocarbons, sulfides and metal-containing ash, etc. These pollutants will seriously affect the environment and people's physical health.

[0003] CO and HC will undergo an oxidation-reduction reaction by an oxidation catalyst (DOC). Currently, the DOC technology can completely oxidize CO and HC. As for PM, it will be completely trapped by a diesel particulate filter (DPF). The NOx pollutants will undergo a catalytic reduction reaction with urea inside a selective catalytic reduction (SCR) device. However, the selective catalytic reduction (SCR) device requires a suitable operating temperature for the catalytic reduction reaction, and the optimal reaction temperature is between 250°C and 450°C. Only through effective thermal management can a high conversion efficiency be obtained. For engines with a displacement of more than 4L, the exhaust gas flow is large and the engine exhaust temperature is high, and the temperature drop from the turbocharger tail pipe to the selective catalytic reduction (SCR) device is small, which can meet the requirements of high conversion efficiency. For small engines with a displacement of less than 4L, it is difficult to increase the exhaust gas temperature without adding an intake throttle valve, and the NOx pollutant emissions cannot be effectively reduced.

[0004] Currently, the mainstream technical route for National VI is the exhaust gas recirculation device (EGR) + intake throttle valve + DOC + DPF + SCR control technology. The EGR is used to control nitrogen oxides (NOx) in the engine. By reducing the raw emissions of the engine and supplemented by a selective catalytic reduction (SCR) converter, the tailpipe NOx is controlled within the National VI limits. However, the configuration of the exhaust gas recirculation device (EGR) + intake throttle valve + DOC + DPF + SCR is relatively complex. Moreover, due to the adoption of the EGR system, an additional intake air flow meter is required to control the EGR valve. In addition to the EGR valve, an EGR cooler also needs to be installed in the EGR system. Since the EGR cooler requires the engine to supply a part of the cooling water and cool the exhaust gas, the requirement for the water supply flow capacity of the water pump is increased. The control of the mainstream route EGR valve requires an intake air flow meter. Currently, the problem of large scatter in both the thermal mode and differential pressure type flow meters for National VI intake air flow meters is inevitable. The thermal mode flow meter is greatly affected by the scatter in the intake system. The pipeline layout, pipe diameter, and air filter back pressure in the intake system will all affect the measurement accuracy of the thermal mode flow meter. Due to the working principle of the differential pressure type flow meter being affected by the change in the diameter of the Venturi tube, the accuracy drift of the intake air flow meter will cause abnormal opening of the EGR valve, thereby affecting the overall EGR rate and the control of nitrogen oxides (NOx). The existing mainstream National VI EGR route has a relatively complex configuration and high cost; there is a risk of coking in the EGR cooler in cold regions; an additional air flow meter needs to be installed for EGR control; therefore, eliminating EGR can reduce the coking risk, eliminate the need for an additional air flow meter, reduce costs, and improve reliability.

[0005] The current mainstream non-EGR route is: DOC + DPF + SCR + ASC + exhaust throttle valve; the exhaust throttle valve is used to control the exhaust gas temperature at low speed and low load, and improve the working temperature and conversion efficiency of the aftertreatment.

[0006] As the publication number: CN100538031C, a diesel engine is provided with a continuously regenerating DPF, and an exhaust throttle valve is provided on the downstream side of the continuously regenerating DPF. The continuously regenerating DPF includes a diesel particulate filter that traps particulate matter in the exhaust gas and a catalyst provided on the upstream side of the diesel particulate filter. The characteristic is that in order to oxidize and remove the particulate matter accumulated on the diesel particulate filter and regenerate the filter, when the diesel engine is operated with a relatively small opening of the exhaust throttle valve, at the end of the regeneration of the diesel particulate filter, after performing an operation to reduce the rotational speed of the diesel engine, the opening of the exhaust throttle valve is increased.

[0007] An exhaust throttle valve needs to be additionally installed, increasing costs. It is necessary to calibrate the throttle valve opening at different loads, which is difficult to control and increases the calibration workload. In particular, for small displacements in light truck projects below 2.3L, the power and torque requirements are small, and the charging efficiency is too low. Currently, there is no better way to increase the exhaust gas temperature of small-displacement non-EGR engines.

[0008] The information disclosed in this background art section is only intended to enhance the overall understanding of the present invention and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to those of ordinary skill in the art. Summary of the Invention

[0009] The technical problem to be solved by the present invention is: how to solve the problems that the current non-EGR method for diesel engines requires an additional exhaust throttle valve, increased costs, and difficult control.

[0010] The present invention achieves the solution to the above technical problems through the following technical means:

[0011] A pollutant control device for a National VI small-displacement non-EGR diesel engine, applied to diesel engines with a displacement below 2.3L, includes a turbocharger turbine, an oxidation catalyst, a particulate trap, and a selective catalytic reducer sequentially connected to the engine exhaust end; the throat area of the turbocharger turbine is greater than 230 mm 3 , and the diameter of the turbine of the turbocharger turbine is less than 44 mm.

[0012] The present invention abandons the use of an intake throttle valve. By adding a turbocharger turbine at the front end of DOC+DPF+SCR and adopting a large-throat turbocharger scheme, the turbine is reduced, the throat is enlarged, and the entropy increase in the turbine increases. The outlet Mach number increases, and the engine exhaust temperature increases. Without installing an exhaust throttle valve, the exhaust temperature at low speed and small load can be increased, achieving the effect of installing an exhaust throttle valve; for diesel engines with a displacement above 2.3L, the charging efficiency is too high. Adopting a small-impeller, small-turbine, large-throat turbocharger scheme will cause blockage in the high-speed region and there is a high risk of turbocharger overspeed on the plateau. For light truck projects below 2.3L, the power and torque requirements are small, and the charging efficiency is too low, which can avoid the above-mentioned blockage and overspeed risks. The exhaust gas flow generated by the engine combustion drives the rotation of the turbocharger turbine, which is the process of turbocharging the turbocharger turbine. The pressurized gas flows into the oxidation catalyst, particulate trap, and selective catalytic reducer. The temperature of the pressurized gas increases, which is beneficial for the selective catalytic reducer to reach the optimal reaction temperature and obtain a higher conversion efficiency. Moreover, the throat area of the turbocharger turbine in the present invention is greater than the throat area of the current 2.3L diesel engine project, and at the same time, the diameter of the turbine of the turbocharger turbine is made smaller to improve the post-treatment exhaust temperature of the vehicle PMES and bench WHTC under low-load conditions and reduce the tailpipe NOx emission limit.

[0013] Preferably, the turbine throat area A is calculated as follows:

[0014]

[0015] where G is the tangential gas velocity at the centroid of the 0-0 cross-sectional area of the turbine housing; ρ t1 : the gas density in front of the turbine;

[0016] Preferably, the formula for calculating the tangential gas velocity at the centroid of the 0-0 cross-sectional area of the turbine housing is as follows:

[0017]

[0018] R T : the distance from the centroid of the 0-0 cross-sectional area to the center of rotation of the supercharger, Gu: the engine intake air flow, D T1 : the turbine diameter, φ T : the velocity coefficient is a constant.

[0019] Preferably, the formula for calculating G T is as follows:

[0020] G T = K G × G L

[0021] where K G : the pulse flow coefficient is a constant, G L : the exhaust gas flow;

[0022] Preferably, the formula for calculating the gas density ρ t1 in front of the turbine is as follows:

[0023]

[0024] P t1 : the gas pressure in front of the turbine, T tl : the exhaust gas temperature in front of the engine turbine, R is a constant.

[0025] Preferably, the throat area of the supercharger turbine is greater than 280 mm 3 .

[0026] Preferably, it further includes a supercharger compressor. The supercharger turbine and the supercharger compressor are coaxially arranged, and the outlet end of the supercharger turbine is connected to the supercharger compressor.

[0027] Preferably, it further includes an intercooler. The outlet end of the supercharger compressor is connected to the intercooler, and the outlet end of the intercooler is connected to the intake end of the engine.

[0028] Preferably, the outlet end of the engine is connected to an exhaust manifold, and the exhaust manifold is connected to the turbocharger turbine.

[0029] The advantages of the present invention are as follows:

[0030] (1) By abandoning the use of an intake throttle valve and adding a turbocharger turbine at the front end of the DOC+DPF+SCR, the exhaust gas flow generated by the engine combustion is used to drive the rotation of the turbocharger turbine. This process is the supercharging process of the turbocharger turbine. The supercharged gas flows into the oxidation catalytic converter, particulate trap, and selective catalytic reducer. The temperature of the supercharged gas increases, which is beneficial for the selective catalytic reducer to reach the optimal reaction temperature and obtain a higher conversion efficiency. Moreover, the throat area of the turbocharger turbine in the present invention is larger than that of the current 2.3L diesel engine project. At the same time, the turbine diameter of the turbocharger turbine is reduced to improve the post-treatment exhaust temperature of the vehicle PMES and bench WHTC under low load conditions and reduce the tailpipe NOx emission limit. Description of the Drawings

[0031] Figure 1 is a schematic structural diagram of the pollutant control device for a national VI small-displacement non-EGR diesel engine according to an embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of the throat of the turbocharger turbine according to an embodiment of the present invention;

[0033] Figure 3 is a schematic diagram of the throat of the turbocharger turbine according to an embodiment of the present invention;

[0034] Figure 4 is a schematic diagram of the large and small diameters of the impeller of the turbocharger turbine according to an embodiment of the present invention;

[0035] Figure 5 is a schematic diagram of the large and small diameters of the turbine of the turbocharger turbine according to an embodiment of the present invention

[0036] Reference numerals in the drawings:

[0037] 1. Engine; 11. Exhaust manifold; 12. Intake manifold;

[0038] 2. Turbocharger turbine; 3. Oxidation catalytic converter; 4. Particulate trap; 5. Selective catalytic reducer 6.; Turbocharger compressor; 7. Intercooler; Detailed Embodiments

[0039] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0040] Embodiment 1:

[0041] As Figure 1 shown, a pollutant control device for a National VI small-displacement non-EGR diesel engine is applied to a diesel engine with a displacement of less than 2.3L, and includes an exhaust manifold 11 connected to the exhaust end of the engine 1 and an intake manifold 12 connected to the intake end; the exhaust manifold 12 is sequentially connected to a turbocharger turbine 2, an oxidation catalytic converter 3, a particulate trap 4, and a selective catalytic reducer 5; at the same time, the turbocharger turbine 2 is coaxially connected to a turbocharger compressor 6, the turbocharger compressor 6 is connected to an intercooler 7, and the intercooler 7 is connected to the intake manifold.

[0042] In this embodiment, the throat area of the turbocharger turbine 2 is greater than 230 mm 3 , and the diameter of the turbine of the turbocharger turbine 2 is less than 44 mm. More specifically, the throat area of the turbocharger turbine is greater than 280 mm 3 , and the diameter of the turbine of the turbocharger turbine 2 is 37 mm.

[0043] The calculation method of the throat area of the turbocharger turbine 2 in this embodiment is as follows:

[0044] The throat area A of the turbine is calculated as follows:

[0045]

[0046] Among them, G: the tangential velocity of the gas at the centroid of the cross-sectional area of the turbine housing; ρ t1 : the gas density in front of the turbine; G T is the gas flow rate; G, the tangential velocity of the gas at the centroid of the cross-sectional area of the turbine housing, is calculated according to the equal circulation, and the calculation formula is as follows:

[0047]

[0048] R T : the distance from the centroid of the cross-sectional area to the rotation center of the turbocharger, Gu: the engine intake air flow rate, which can be measured by the intake air flow measurement unit on the engine 1, DT1: the large and small diameters of the turbine, φ T : the velocity coefficient is a constant, and the constant is usually selected as 0.92.

[0049] Among them, G TThe calculation formula is as follows:

[0050] G T =K G ×G L

[0051] Wherein, K G : The pulse flow coefficient is a constant, and the constant is 1.03. G L : The exhaust gas flow rate can be measured by the exhaust gas flow measurement unit on the engine 1;

[0052] Wherein, the density ρ of the gas in front of the turbine t1 The calculation formula is:

[0053]

[0054] P t1 : The gas pressure in front of the turbine, T tl : The exhaust gas temperature in front of the engine turbine, which is measured by the temperature measurement unit on the engine. R is the gas constant, and here it is taken as 287 J / kg·K.

[0055] Through the above, the turbine throat area used can be calculated through the turbine diameter, engine intake air flow rate, exhaust gas flow rate, etc.

[0056] In this embodiment, by abandoning the use of the intake throttle valve and adding a supercharger turbine at the front end of the DOC+DPF+SCR, the exhaust gas generated by the combustion of the engine 1 flows out through the exhaust manifold 12 and enters the supercharger turbine 2, driving the supercharger turbine 2 to rotate. The supercharger turbine 2 and the supercharger compressor 6 are coaxially arranged. Therefore, when the supercharger turbine 2 rotates, the supercharger compressor 6 also rotates accordingly. The supercharger compressor 6 can compress the gas entering the engine and then enter the engine. This process is the process of supercharging by the supercharger turbine 2. The supercharged gas flows into the oxidation catalytic converter 3, the particulate trap 4, and the selective catalytic reduction converter 5. The temperature of the supercharged gas rises, which is beneficial for the selective catalytic reduction converter 5 to reach the optimal reaction temperature and obtain a higher conversion efficiency.

[0057] The throat area of the supercharger turbine 2 in this embodiment is larger than the throat area (230mm 3 ) of the current 2.3L diesel engine project. At the same time, the turbine diameter of the supercharger turbine 2 is reduced to improve the post-treatment exhaust gas temperature of the vehicle PMES and the bench WHTC under low load conditions and reduce the tailpipe NOx emission limit.

[0058] In this embodiment, a supercharger with a large throat is adopted. The turbine is reduced, the throat is enlarged, and the entropy increase in the turbine increases. The outlet Mach number increases, and the exhaust gas temperature of the engine rises. Without installing an exhaust throttle valve, the exhaust gas temperature at low speed and low load can be increased, achieving the effect of installing an exhaust throttle valve. However, for diesel engines with a displacement of more than 2.3L, the charging efficiency is too high. Adopting a supercharger with a smaller impeller diameter inside the compressor and a large throat will cause blockage in the high-speed region and there is a high risk of supercharger overspeed at high altitudes. Therefore, this solution is more suitable for light truck projects with a displacement of less than 2.3L. For light truck projects with a displacement of less than 2.3L, the power and torque requirements are small and the charging efficiency is too low, so the above-mentioned blockage and overspeed risks can be avoided.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A pollutant control device for a China VI small-displacement non-EGR diesel engine, which is applied to diesel engines with a displacement below 2.3L, and is characterized in that, It includes a supercharger turbine, an oxidation catalytic converter, a particulate trap, and a selective catalytic reducer that are sequentially connected to the exhaust end of the engine; the throat area of the supercharger turbine is greater than 230 mm 3 , and the diameter of the turbine of the supercharger turbine is less than 44 mm; the turbine throat area A is calculated as follows: Among them, G: the tangential gas velocity at the centroid of the cross-sectional area of the turbine box at the 0-0 section; ρ t1 : the gas density in front of the turbine.

2. The pollutant control device for a China VI small-displacement non-EGR diesel engine according to claim 1, and is characterized in that, Among them, The calculation formula for the tangential gas velocity at the centroid of the cross-sectional area of the turbine box at 0-0 is as follows: R T : Distance from the centroid of the sectional area at the 0-0 section to the center of rotation of the supercharger, Gu: Engine intake air flow rate, D T1 : Turbine diameter, φ T : The velocity coefficient is a constant.

3. The pollutant control device for a China VI small-displacement non-EGR diesel engine according to claim 1, and is characterized in that, Among them, G T The calculation formula is as follows: G T = K G × G L Among them, K G : the pulse flow coefficient is a constant, G L : the exhaust gas flow rate.

4. The pollutant control device for a China VI small-displacement non-EGR diesel engine according to claim 1, and is characterized in that, Among them, Gas density ρ before turbine t1 The calculation formula is as follows: P t1 : Gas pressure before turbine, T tl : Exhaust gas temperature in front of engine turbine, R is a constant.

5. The pollutant control device for a China VI small-displacement non-EGR diesel engine according to claim 1, and is characterized in that, The throat area of the supercharger turbine is greater than 280 mm 3 .

6. The pollutant control device for a China VI small-displacement non-EGR diesel engine according to claim 1, and is characterized in that, It also includes a supercharger compressor. The supercharger turbine and the supercharger compressor are arranged coaxially, and the outlet end of the supercharger turbine is connected to the supercharger compressor.

7. The pollutant control device for a China VI small-displacement non-EGR diesel engine according to claim 6, and is characterized in that, It also includes an intercooler. The outlet end of the supercharger compressor is connected to the intercooler, and the outlet end of the intercooler is connected to the intake end of the engine.

8. The pollutant control device for a China VI small-displacement non-EGR diesel engine according to claim 1, and is characterized in that, The outlet end of the engine is connected to an exhaust manifold, and the exhaust manifold is connected to the supercharger turbine.

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